[clang] [clang] Support constexpr bitcasts between equal-size vector and integer types (PR #167016)

[Timm Baeder via cfe-commits]

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@@ -17724,7 +17078,24 @@ bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) {
   case CK_HLSLAggregateSplatCast:
     llvm_unreachable("invalid cast kind for integral value");
 
-  case CK_BitCast:
+  case CK_BitCast:{
+  APValue Sub;
+  if (!Evaluate(Sub, Info, E->getSubExpr()))
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tbaederr wrote:

We know the types before evaluating the subexpression, so we don't have to do this unless the sizes match.

https://github.com/llvm/llvm-project/pull/167016